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Re: Data visibility for returning statement - Mailing list pgsql-docs

From David G. Johnston
Subject Re: Data visibility for returning statement
Date
Msg-id CAKFQuwZva2EhVxeyVEtYyDs9RoOzf3XWzNUEpJ==FBSifSHoAw@mail.gmail.com
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In response to Data visibility for returning statement  (PG Doc comments form <noreply@postgresql.org>)
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On Sat, Apr 26, 2025 at 5:50 AM PG Doc comments form <noreply@postgresql.org> wrote:
The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/17/dml-returning.html
Description:

Today I found a pretty special use-case for the "RETURNING" functionality,
which I cannot find documentation for?
If you have a statement as follows:
UPDATE persons SET name = 'Bob' WHERE id = 4
RETURNING (SELECT name FROM persons WHERE id = 4)
The returning data will be whatever the value was before the row was
modified. This differs from if I were to "RETURNING name". I found this to
be interesting and could possibly warrant some kind of explanation in the
documentation?


I would not want to encourage that form of query.  The novelty is more problematic than the brevity.  Plus, repetition.

with new_p as ( update persons set name = 'Bob' returning name where id = 4)
select 
old_p.id as id,
old_p.name as old_name,
new_p.name as new_name
from persons as old_p
join new_p on new_p.id = old_p.id

And now that we actually allow references to "new" and "old" in v18 that form is also obsolete and you can do this directly.

David J.

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